Secondary batteries are batteries in which the chemical reaction that generates electrical energy is electrically reversible. Commonly used secondary cell (“rechargeable battery”) chemistries are lead-acid (such as a conventional automobile battery), nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer). These batteries offer the benefit of repeated use and recharging, thereby extending the life of the battery as compared to a conventional primary battery, in which the electricity-producing chemical reaction is a one-way reaction that eventually consumes the component materials.
In recent years, the use of lithium-ion (Li-ion) batteries has expanded from small appliance applications to larger scale applications. Most recently, Li-ion batteries have been considered for use in electric vehicles, such as gas-electric hybrid automobiles and electric-only automobiles. Although such batteries are effective in many of these applications, insufficient thought appears to have been given to the availability of lithium, as compared to the world demand for lithium for use in batteries for conventional purposes, as well as for transportation.
World reserves of lithium are currently estimated to be on the order of about twenty-eight million tons, making lithium one of the more uncommon elements on the Earth's surface. Only about four hundred thousand tons of lithium are located within the borders of the United States, with the bulk of the world's reserves being located within Bolivia, China, and Russia. As demand for lithium continues to increase worldwide, one can readily predict that other countries and regions may seek to control their supply of lithium, either for their own internal use or to inflate market price.
To have adequate capacity for practical use by consumers, a typical plug-in hybrid car requires a battery pack weighing at least six hundred pounds, at least forty pounds of which is lithium. To convert the entire population of three hundred million automobiles in the United States to a lithium-based battery system would require about six million tons of lithium, exceeding the U.S. supply of lithium by a factor of fifteen to one.
Extrapolating the situation worldwide to a population of roughly eighteen times that of the United States, a conservative estimate for lithium demand would be approximately sixty million tons, thus exceeding the global supply of lithium by a factor of more than two to one.
Because lithium is fairly rare, some battery manufacturers have sought to produce effective battery systems using more abundant materials, such as magnesium, which has been explored with some degree of success. Magnesium batteries have substantial promise as rechargeable systems for many battery applications, including the electric car, portable electronics, and tools. Whereas some alkali metals (such as lithium) are highly flammable and may be poisonous, alkaline earth metals (such as magnesium) are easy to process and exhibit stable behavior. Additionally, magnesium is the third most common metal that can remain unprotected in the Earth's atmosphere, with the world reserves of magnesium being on the order of at least eight billion tons. Moreover, vast amounts of magnesium salts are dissolved in sea water and recoverable therefrom.
As compared to a lithium battery, a magnesium battery may require approximately twice as much metal—that is, about eighty pounds per battery pack. With this greater requirement, the world demand for magnesium batteries (for vehicle usage alone) could possibly reach as much as twelve million tons. However, because of the abundance of magnesium, the global supply of magnesium far exceeds the demand by a factor of at least six hundred fifty to one.
Accordingly, a need exists in the industry for a durable battery made of readily abundant materials, which may be easily assembled and repeatedly recharged. The present disclosure addresses such a need.